Power busway used within multi-phase electric power distribution systems generally consist of long, rectangular bars of copper or aluminum material with each individual bar electrically insulated to maintain electrical isolation between the individual phases as well as between the phase conductors and the neutral conductors. In accordance with state and local electrical codes, a ground conductor must be associated within the busway power distribution system. U.S. Pat. No. 4,673,229 entitled "Electrical Distribution System With an Improved Housing" describes a busway system that incorporates a ground bus within the busway housing. Other known busway systems use the conductive property of the steel busway enclosure to provide the required ground conductor.
To maintain electrical integrity between the separate bus conductors within the busway system which include so-called "feeder" and "plug-in" systems, while providing intimate thermal transfer between the bus conductors and the heat radiating support structure, one or more bolts are used to tightly support the bus conductors within the housing. The insulative coating on the individual bus conductors maintains the electrical integrity while the pressure applied by means of the connective bolt ensures good heat conductivity between the bus bars as well as between the bus bars and the metal support structure. U.S. Pat. No. 3,555,293 entitled "Bus Duct" describes the use of a pair of side plates that are bolted together on opposite sides of the enclosed bus conductors.
It has heretofore been the practice in the art of busway construction to avoid contacting any part of the bus conductors with the bolt or bolts that support the busway housing since the busway housing is generally at ground potential.
The use of an epoxy resin as an insulative coating for bus conductors has beneficially resulted in busway systems having good thermal transport from the bus conductors to the busway housing while maintaining the necessary electrical insulating properties therebetween.
The use of a ferrous metal housing, such as cold rolled steel for example, has both thermal and weight disadvantages. The electromagnetic properties induce eddy currents within the busway housing when the bus conductors are carrying currents in excess of several hundred amperes. The poor electrical conductive property of the ferrous metal further increases the thermal load on the busway system when ground currents are carried by the busway housing. The relatively low thermal conductivity of the ferrous metal housing reduces the rate at which the heat load generated within the housing is dissipated to the surrounding atmosphere.
The use of non-ferrous metals such as aluminum and copper has heretofore been shunned because of the relatively poor structural support properties inherent within such metals. The use of separate insulation strips between the individual bus bar conductors has heretofore discouraged bolting the bus conductors directly to the support housing because of the difficulty in aligning the holes through the insulation strips with the holes through the bus conductors and the support housing.
It has since been determined that aluminum-magnesium alloys, in extruded form, have sufficient strength properties to support copper or aluminum bus conductors, when the bus conductors are directly bolted to their respective support housing. The application of an insulative coating directly to the surface of the bus conductors provides sufficient electrical insulation to holes punched through the bus conductors without allowing electrical conduction to occur between the individual bus conductors themselves. One purpose of the instant invention is to describe a structurally sufficient busway power distribution system which includes a support structure that is light weight, and exhibits excellent thermal and electrical conductive properties.